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Description of problem:
While testing Veritas NetBackup 5.1 MP3 on RedHat 3 x86_64 we ran across this issue. The system locks up when beginning to write to a second tape path. This forces a reboot and the system throws a kernel panic:
System Trace
------------
{pci_map_sg+227}
{:qla2300: qla2x00_64bit_start_scsi+888}
{:qla2300: qla2x00_queuecommand+1297}
{:qla2300: qla2x00_next+532}
{:qla2300: qla2x00_queuecommand+1297}
{scsi_mod: scsi_times_out+0}
{:scsi_mod: scsi_dispatch_cmd+640}
{:scsi_mod: scsi_request_fn+1041}
{:scsi_mod: __scsi_insert_special_req+127}
{:scsi_mod: scsi_insert_special_req+31}
{:scsi_mod: scsi_do_req_Rsmp_ff69bbf9+350}
{:st: st_sleep_done+0}
{:st: st_do_scsi+310}
{:st: read_tape+260}
{__get_free_pages+16}
{:st: st_read+829}
{:sys_read+178}
{ia32_syscall+103}
Code:
0f 0b b6 7c 2d 80 ff ff ff ff 2b 00 eb 5d 48 8b 4b 08 48 85
Kernel panic: Fatal exception
The system shows this panic everytime it is booted until the device is unattached from the host.
Version-Release number of selected component (if applicable):
How reproducible:
Sometimes
Steps to Reproduce:
1. Install RedHat 3 x86 64_bit
2. Install NetBackup 5.1 MP3
3. Create a policy that will write to two devices at the same time
4. Fire off the policy and the system locks
5. Reboot to see kernel panic
6. Unplug the device or else the system will panic everytime it boots
Actual Results: System locked.
Kernel panic.
Expected Results: Should keep writing to tapes.
Additional info:
This issue was seen on two different machine types including a Sun Fire V20z (dual Opteron's) and Supermicro (dual EM64T's). The exact same machines were loaded with the 32-bit build of RH3 and worked without a problem.
Tried recreating this using tar and mt but the system does not lock. The 32-bit Linux build of NetBackup was used on both RH3 32-bit, which didn't show this issue, and RH3 x86_64 which did. This, and the system trace make us believe that it is not a NetBackup issue. Qlogic and Emulex have investigated the problem since it was their driver that originally called st but they have not found anything in their debug logs that indicate an issue with their driver.
Found a similar bug (but different) here:
https://bugzilla.redhat.com/bugzilla/process_bug.cgi
Sebastien BLAISOT (sblaisot@pagesjaunes.fr)
Comment #14 has the same panic trace that I had.

A new set of test kernel RPMs have been posted to the same place as before.
These include the fix for the sg+st write bug and one other tweak that might
help with this problem. Please test these out and let me know the results.

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.
http://rhn.redhat.com/errata/RHSA-2006-0144.html